1. Field of the Invention
The present invention relates to an electron beam irradiation apparatus and an electron beam irradiating method, for example used in master recording for an optical disk.
2. Description of the Related Art
In recent years, a much higher density has been demanded for optical disks, so that a finer formation of recording pits is needed to accomplish thereof. On this account, in the production of a master disk of an optical disk, there has been proposed an apparatus for irradiating a master disk with an electron beam instead of conventional laser beams for recording.
In this electron beam irradiation apparatus, an electron beam irradiation in a vacuum environment is needed to prevent the electron beam from colliding against gas molecules to be scattered. In this case, when the entire electron beam irradiation apparatus is placed in the vacuum environment, a large vacuum space and a large exhaust means will be needed, resulting in a large and expensive apparatus.
To avoid this, the applicant previously proposed an electron beam irradiation apparatus in a partial vacuum method where only a portion irradiated with the electron beam is placed in a vacuum condition, in a Japanese Patent Application No.2000-57374.
Specifically, this electron bean irradiation apparatus is structured in such a way that a static pressure floating pad is connected to an outlet of the electron beam of a vacuum chamber containing an electron bean column, the static pressure floating pad is attached without contacting and with a little gap of the order of several micro meters (xcexcm) to the master disk by a suction through an exhaust means and a supply of compressed gas through an air supply means, and in this condition, the electron beam emitted from an electron gun passes through an electron beam path in the center of the static pressure floating pad to be irradiated on the master disk.
In the electron beam irradiation apparatus structured in this way, when a replacement operation of the master disk is executed, the static pressure floating pad needs to be released from the master disk. In this case, the static pressure floating pad is completely separated from the master disk, so that the air flows through the electron beam path of the static pressure floating pad into the vacuum chamber and the electron beam column is exposed to open air.
Accordingly, the workability is extremely bad in such a way that a gate valve of the electron beam column needs to be closed to protect the electron gun while maintaining the previous high vacuum prior to releasing the static pressure floating pad, and the power needs to be turned off in order to protect the exhaust means (vacuum pump) for vacuumizing the vacuum chamber.
Additionally, when a vacuum system is restarted after the master disk is replaced, several hours are to be spent until that the degree of vacuum in the vacuum chamber is increased to the extent that the irradiation of the electron beam is not disturbed, and the degree of vacuum is stabilized. Therefore, this is an extremely inefficient system in such a manner that waiting time is longer than the time for recording the master disk by the electron beam irradiation.
In another aspect, because the vacuum chamber falls under the open-air condition every time when the master disk is replaced, there has been a problem of contamination in the vacuum chamber and the electron beam column due to the result of sucking dust in the air.
In light of these problems, it is an object of the present invention to solve the above-mentioned problems in a manner that the necessary vacuum can be maintained in the vacuum chamber even in the condition where the static pressure floating pad is separated from the subject to be irradiated (master disk) in the electron beam irradiation apparatus in a partial vacuum method.
To solve the aforementioned problems, the present invention is characterized in that an electron beam irradiation apparatus is structured with a static pressure floating pad connected to a vacuum chamber containing an electron beam column and in a condition that the static pressure floating pad is attached to a subject to be irradiated without contacting, an electron beam is irradiated on the subject to be irradiated through an electron beam path of the static pressure floating pad, wherein a vacuum seal valve is provided with a piston to open and close the electron beam path inside of the static pressure floating pad and the vacuum seal valve is formed with a cross section in a round shape. Additionally, in this structure, the vacuum seal valve is preferably formed with a cross section in a round shape, and in a tapered shape with a narrow tip and a wide root. The vacuum seal valve may also be structured such that the cross section is in the round shape, an elastic material is attached to the tip thereof, and the elastic material is radially expanded by a pushing force of the valve to block the electron beam path.
In the electron beam irradiation apparatus of the present invention structured in this way, when the static pressure floating pad is released from the subject to be irradiated, the vacuum valve is activated to close the electron beam path so as to accomplish vacuum-sealing, whereby the vacuum chamber and the electron beam column can be maintained in the desired degree of vacuum. Specifically, in the present invention, the vacuum seal valve is formed with the cross section in the round shape to facilitate high-precision machining. Moreover, the vacuum seal valve is formed in the tapered shape with the narrow tip, so that a high vacuum seal with almost no gap can be accomplished. Additionally, in the structure that the elastic material on the tip is radially expanded by the pushing force of the valve to block the electron beam path, the degree of vacuum in the vacuum chamber and the electron beam column can reliably be maintained.